1. Field of the Invention
The present invention relates in general to catalytic converters installed in an exhaust system of an internal combustion engine, and more particularly, to catalytic converts of a type called "manifold converter" which is directly connected to output ports of an exhaust manifold of the internal combustion engine.
2. Description of the Prior Art
In order to clarify the task of the present invention, a conventional manifold converter will be described with reference to FIGS. 6 to 8, which is shown in Japanese Utility Model First Provisional Publication 3-83315.
In FIGS. 6 to 8, there is shown the conventional manifold converter which is generally designated by numeral 1. As is seen from FIGS. 7 and 8, the manifold converter 1 is connected to outlet pipes 5a, 5b, 5c and 5d of an exhaust manifold 5 which is mounted to one side of an internal combustion engine 3. As is seen from FIG. 7, the manifold converter 1 is vertically held by the exhaust manifold 5 and has an output port from which an exhaust pipe 19 extends toward a muffler (not shown).
As is seen from FIGS. 7 and 8, the manifold converter 1 comprises a housing 9 having an oval cross section. The housing 9 is constructed of two metal shells 9a and 9b which are assembled to constitute a vessel structure. Within an enlarged container part 11 (see FIG. 8) of the housing 9, there is tightly installed a catalyser carrier unit 7 which has an oval cross section. The housing 9 has respective diffusers 13 and 15 at upstream and downstream portions thereof with respect to the catalyser carrier unit 7. The upstream diffuser 13 has gas inlet ports 13a connected with the outlet pipes 5a, 5b, 5c and 5d of the exhaust manifold 5, while the downstream diffuser 15 has a gas outlet port 15a connected with the exhaust pipe 19. The gas outlet port 15a is formed with a flange 17.
Along upper and lower peripheral edges of the catalyser carrier unit 7, there extend respective shock absorbing members 21 and 23 which are pressed against diametrically reduced upper and lower portions of the container part 11. Thus, the catalyser carrier unit 7 is held in the container part 11 through the shock absorbing members 21 and 23.
Furthermore, between the catalyser carrier unit 7 and the container part 11, there are installed corrugated support members 25a and 25b and a foamed sealing mat 27. Due to provision of the sealing mat 27, the clearance between the catalyser carrier unit 7 and the container part 11 is hermetically sealed, so that gas fed to the upstream diffuser 13 is forced to travel through only the catalyser carrier unit 7.
As is seen from FIGS. 6 and 7, a shroud 29 is fixed to the housing 9 at an outer side thereof which is remote from the engine 3. Although not shown in the drawings, a plurality of bosses are integrally formed on the housing 9 to define a certain air clearance between the shroud 29 and the outer surface of the housing 9.
Under operation of the engine 3, exhaust gas from the engine 3 is led into the exhaust manifold 5 and then led into the manifold converter 1. The gas fed to the converter 1 is purified by the catalyser on the carrier unit 7 and then led to the exhaust pipe 19.
However, due to its inherent construction, the above-mentioned conventional manifold converter 1 has the following drawbacks.
That is, during operation of the engine 3, the housing 9 of the manifold converter 1 is subjected to heat expansion due to the marked heat generated in the converter 1. While, when the engine is at a standstill, the housing 9 of the converter 1 is cooled and thus contracts. Thus, long use of the converter 1 while being attacked by such expansion and contraction tends to cause the container part 11 of the housing 9 to have a permanent expansion which brings about a clearance between the foamed sealing mat 27 and the container part 11. The clearance thus produced constitutes an undesired bypass passage for the gas in the converter 1. Furthermore, such clearance lowers the stability with which the foamed sealing mat 27 is seated in the right position. In fact, in severe cases, due to marked gas pressure applied to such unstable sealing mat 27, the mat 27 is scattered in the gas.